The U.S. is running low on adolescents: The number of young people graduating from high school will plateau or fall in coming years, according to the new Knocking at the College Door report.

The racial/ethnic mix of public high school graduates will shift: The number of Hispanic graduates is expected to increase by 50 percent and and Asian/Pacific Islander grads by 30 percent through 2025, while fewer whites and blacks will be going through school.

According to one respected tally, just under 55 percent of students who entered college in 2010 had earned degrees after six years – an increase of two percentage points since 2009.

For higher education institutions to continue at that pace or boost it, they’ll need to find new ways of educating a student body increasingly composed of people who are the first in their family to enter college.

With fewer 18-year-olds whose parents can pay for a private residential college, I predict many second- and third-tier colleges will fold. They’re very expensive, they don’t graduate a high percentage of their students and young people are becoming wary of college debt.

Anthony Sobowale failed high school chemistry, then passed after three days of “online credit recovery.” Now he’s struggling with organic chem at Georgia State. Photo: Bob Andres/Atlanta Journal-Constitution

In October, President Obama announced that the national high school graduation rate had reached an all-time high in 2015. Yet that same year, the percentage of high school seniors ready for college-level reading and math declined to 37 percent. In other words, as graduation rates rise, other metrics of student achievement are falling, raising questions about how schools are getting more students to graduate.

Noonan worked for a Douglas County, Georgia school district that raised its graduation rate — but not student achievement. As an OCR classroom manager, he was told to ensure that students earned at least 80 percent on multiple-choice quizzes and tests by giving them as many tries as they needed. The questions and answer choices were repeated, in the same order.

In addition, teachers provided “answer checks,” writes Noonan.

When students finished the first attempt on a quiz or test, they call upon the teacher for a “check.” He or she pulls up the student’s answers, reviews them, and informs the student which questions are incorrect. The student then changes his or her answers before submitting the assessment for a grade.

Most students didn’t pay attention to the lessons, writes Noonan. They knew they could guess their way to a passing score.

As Douglas County’s graduation rate rose, so did the percentage of graduates who required college remediation.

Higher performing nations teach fewer math topics in greater depth, Andreas Schleicher, who runs the test, told journalists. Students master a topic and then move on, rather than cycling back to the same concept each year, he said.

PISA results matter, writes Robert Rothman. “PISA is designed to measure how well students can apply what they have learned to real-world problems.” In a follow-up study, Canadian students’ results correlated with their success in college and the job market.

The usual excuses don’t apply, he argues. U.S. students aren’t more likely to live in poverty than children in other OECD countries. U.S. 15-year-olds are slightly less likely to be enrolled in school.

Hong Kong has lots of poverty — and high scores for all students. Estonia also is an equity champion.

The U.S. improved on measures of equity, notes Amanda Ripley in the New York Times. “In 2006, socioeconomic status had explained 17 percent of the variance in Americans’ science scores; in 2015, it explained only 11 percent, which is slightly better than average for the developed world.”

PISA scores don’t correlate with education spending, Ripley observes. The U.S. spends more than most OECD countries for average or below-average performance. Malta spends about the same — and outperforms the U.S.

Luxembourg is the biggest spender, with mediocre results, followed by Switzerland, which has high scores. Taiwan, which spends less than average, and Singapore, which spends more, have similar, very high math scores.

Ripley summarizes what matters:

Generally speaking, the smartest countries tend to be those that have acted to make teaching more prestigious and selective; directed more resources to their neediest children; enrolled most children in high-quality preschools; helped schools establish cultures of constant improvement; and applied rigorous, consistent standards across all classrooms.

“I’m confident the Common Core is going to have a long-term impact,” Schleicher said. “Patience may be the biggest challenge.”

Shawn Sheehan won “teacher of the year” honors in Oklahoma, but earns less than novice teachers in many other states. Photo: Oklahoma Department of Education

Shawn Sheehan, Oklahoma’s teacher of the year, has six years of experience as a high school math teacher and a master’s degree, writes Matt Barnum on The 74. Sheehan earns $35,419 year, or just over $38,000, including benefits.

The average starting salary in the state is just over $31,000, among the lowest in the country. A Tulsa teacher with a master’s degree and 13 years’ experience still makes under $40,000; a teacher with a doctorate, National Board Certification, and 33 years’ experience makes just less than $60,000.

South Dakota and Mississippi, which pay even less, are raising teacher pay. Yet, 59 percent of Oklahoma voters rejected a ballot initiative that would have raised the sales tax to boost teacher pay by $5,000 a year.

When children in Classroom A and Classroom B show the same improvement on their math tests, Teachers A and B get the same evaluation score, and the assumption is that both teachers excel at the same things.

But that assumption may be entirely wrong. Teacher A is a rock star when it comes to imparting math content while Teacher B is not, but Teacher B excels at getting students to persevere when they hit obstacles. So the Classroom A students did well on their tests because they knew the content, while the Classroom B kids did well because they didn’t give up easily and reviewed their answers.

Matthew A. Kraft, who works at Brown, and David Blazar, who works at Harvard, “used student surveys and test score results and pored through hours of video of teachers at work in four urban school districts,” writes Kolodner.

They examined four measures of students’ skill that have been demonstrated individually to predict future academic success and job prospects – high math scores, good behavior, happiness in class and perseverance in the face of difficulty. Their research looked at whether “good teachers” were indeed successful at improving all four of these outcomes.

It turns out they’re not.

“What we find is that teachers who are successful at raising test scores are not [not necessarily] the teachers best at improving behaviors,” said Blazar.

Happy students are more likely to have higher test scores. the researchers found. “However, teachers who improve test scores do not always make students happy in class.”

If distinct teaching skills can be analyzed, they can be taught to new teachers, said Blazar. “We have millions and millions of teachers who work in classrooms, and we do a disservice to the profession if we say we’re only going to try to find those teachers who have that natural spark, when we have evidence that these skills are teachable.”

Is football too dangerous for teens HBO’s Real Sports looks at the risks of head trauma — 17 players have died in the last three years — and at USA Football’s safety initiative, “Heads Up Football.”

“We believe in hitting a lot,” says John Collins, coach of the San Antonio Predators. His players practice full-contact hitting for 90 minutes a day, three times the recommended limit.

Dartmouth Coach Buddy Teevens has cut concussions from 20 a year to two by banning contact tackling in practices. Players tackle sleds and dummies. All eight Ivy League football coaches voted year to ban full-contact tackling in practices, reports Ed Week.